With E-Z Pass transponder on the windshield, you should know what you're about to pay; whatever it is, it's going up.

Despite the high number of drivers in Northern Virginia who already have an E-Z Pass transponder, when the HOT-Lanes open on the Beltway, there will be pressure for many more drivers to subscribe.

VDOT is now proposing to tack on an additional $1 a month fee for each E-ZPass transponder. Note that is per transponder, not per account, so in a household with multiple cars and multiple transponders, the additional annual charge could be $36, $48 or $60.

There are 900,000 transponders in use in Virginia now, with an expected need for more than 400,000 more coming with the new I-495 Express Lanes.

Driving through the E-ZPass lane on the Dulles Toll Road without stopping while cars without a transponder line up to slog through is one advantage. The two other places one can use the E-ZPass in Northern Virginia are the Dulles Greenway and, soon, the "express lanes" on the Beltway.

One of the disadvantages of using the E-ZPass is that you seldom know how much you are paying, and it's significant. Signs with full information about tolls are few and far between, and so far nonexistent on some roads.

Motorists will need an E-ZPass transponder to ride in the Beltway express lanes. Vehicles with three or more people will be able to drive in the express lanes for free if they have a Flex transponder which has a switch that identifies carpoolers, but which also costs more than a regular transponder.

It is worth noting that 100 percent of the tolls from the Beltway HOT-lanes will be collected by the private company that is building them, without any revenue sharing with the Commonwealth. If it is really VDOT's responsibility to maintain the system to collect those tolls, then that is a failure in the crafting of the contract to build the lanes. Apparently all E-ZPass account holders will be paying for the contractor's collection of funds.

Meanwhile, we're still not sure what it will cost to drive in the express lanes, but we do know that the amount will vary depending on traffic. We can only hope that signs will make it clear how much it will cost.

Today VDOT approved four new signs for the Greenway that will at least let drivers know how much they are paying. The answer is more than $5 each way, not counting the new fee per transponder.

VDOT will not hold public hearings on this, although it should. It will be accepting emailed comments. Visit www.virginiadot.org/e-zpass or submit comments directly to vdotinfo@vdot.virginia.gov.